Interstory drift ratio associated with performance objectives for shallow‐buried multistory and span subway stations in inhomogeneous soil profiles

Abstract

The interstory drift ratios (IDRs) associated with the performance objectives for the underground structure are not well defined. In this paper, four levels of performance objectives are defined for shallow-buried subway station structure: operational, immediate occupancy, life safety, and collapse prevention. In order to develop IDRs corresponding to these performance objectives, 18 subway station structures were selected for this study. Pushover analyses were conducted using three-dimensional finite-element models considering two conditions of seismic loading: vertical and horizontal ground motions; and horizontal ground motion only. Shear-displacement capacity curves of the 18 subway station structures were obtained, and IDR limits were defined for each structure based on the relationship between the capacity curves and performance objective. Statistical analysis of the results demonstrated that the IDR limits considering the vertical ground motion (characterized by the same frequency with horizontal component) are smaller than that without consideration of the vertical ground motion. Based on these results, the IDR limit of 0.05%, 0.21%, 0.46%, and 0.72% is assigned for the four performance levels, respectively, for rectangular frame underground structures. The performance evaluation applied to Daikai station based on the proposed limits is found to be consistent with the actual postearthquake damage observations. The proposed limits of IDR could provide some guidance to the seismic design of underground structures, and could form the basis for developing appropriate performance limits for seismic provisions in design codes relevant to underground structures. K E Y W O R D S interstory drift ratio, performance objective, rectangular frame, underground structure, vertical ground motion 1 INTRODUCTION The performance-based seismic design (PBSD) approach intends to achieve defined performance objectives for the seismic design of the structure in a future earthquake. Federal Emergency Management Agency (FEMA) report FEMA-273, 1 FEMA-274 2 introduced the first PBSD procedure, which was aimed at seismic reinforcement of existing buildings, and

Effects of axial compression ratio on seismic behavior of shallow‐buried rectangular stations: Hybrid simulation and quasi‐static test

“…The specified seismic drift ratio limits for rectangular stations are prescribed as 0.1%, 0.37%, 0.77%, and 1.10% for operational, immediate occupancy, life safety, and collapse prevention performance levels without considering vertical ground motion. 68 Based on the quasi-static test results obtained from this study, it is evident that when the drift ratio exceeds 1.10%, the damping ratio significantly increases while stiffness decreases notably. When the axial compression ratio of a column is 0.40, the applied load of the column specimen enters the descending phase, consistent with the suggested drift ratio limit of 1.10% for collapse prevention performance level.…”

Developments in Seismic Vulnerability Assessment of Tunnels and Underground Structures

“…Four damage states were defined, using the interstory drift ratio θ as EDP. The thresholds of damage states were defined following Du et al [92], who performed a series of pushover analyses on 18 actual subway stations found in several cities in China. Stations of various shapes (i.e., two story, two spans; two story, three spans; three-story, three spans) were examined, with local site conditions accounted for in the pushover analyses.…”

“…The maximum interstory drift ratio θ was used as EDP. Five damage states were defined, namely normal operational (NO), immediate operational (IO), reparable operational (RO), irreparable (IR) and complete collapse (CC), with the relevant thresholds being defined as per Du et al [92] and Zhang et al [93]. Based on the analyses results, analytical fragility curves were proposed using Sustained Maximum Acceleration (SMA) as IM for the assessment of the subway station in soil classes I and II, and the Velocity Spectrum Intensity (VSI) as IM for the assessment of the subway station in soil classes III and IV.…”

“…Some studies used 2D numerical models of the examined ground structure configurations to perform pushover analyses, to estimate the structural capacity of, and set the thresholds for, the damage states to develop fragility functions. In most cases the general-purposed FE code ABAQUS was employed to perform the analyses (i.e., more than half of the studies) [56,[63][64][65][66]82,84,85,[89][90][91][92][93][94]. Other FE codes, such as PLAXIS 2D [61], MIDAS [51,60], and SAP2000 [79,80] were also used.…”

“…In some studies, only the structure was modeled as a frame subjected to deformation patterns, replicating the ground shaking effect [85], while other studies proposed the use of 2D numerical models of the ground structure configurations [82,84], also accounting for the effect of the vertical component of ground shaking. Du et al [92] performed a series of pushover analyses using 3D numerical models of actual subway stations, in real sites, to estimate the interstory drift thresholds for distinct performance (limit) states. The analysis approaches that also employ the ground are considered more efficient in replicating soil-structure interaction effects on the response and, hence, on the vulnerability of tunnels and embedded structures (e.g., distributions of earth pressures acting on the structure, effect of soil yielding on the structure).…”